Synergy between Palladium Single Atoms and Nanoparticles via Hydrogen Spillover for Enhancing CO2 Photoreduction to CH4

Selective photoreduction of carbon dioxide (CO2 ) into carbon-neutral fuels such as methane (CH4 ) is extremely desirable but remains a challenge since sluggish multiple proton-electron coupling transfer and various C1 intermediates are involved. Herein, a synergistic function between single Pd atoms (Pd1 ) and Pd nanoparticles (PdNPs ) on graphitic carbon nitride (C3 N4 ) for photocatalytic CO2 methanation is presented. The catalyst achieves a high selectivity of 97.8% for CH4 production with a yield of 20.3 µmol gcat.-1 h-1 in pure water. Mechanistic studies revealed that Pd1 sites activated CO2 , while PdNPs sites boosted water (H2 O) dissociation for increased H* coverage. The H* produced by PdNPs migrate to the Pd1 sites to promote multiple proton-electron coupling transfer via hydrogen spillover. Moreover, the adjacent Pd1 and PdNPs effectively stabilized intermediates such as *CHO, thereby favoring the pathway for CH4 production. This work provides a new perspective into the development of selective photocatalytic CO2 conversion through the artful design of synergistic catalytic sites.